1. Field of the Invention
The present invention relates to semiconductor device fabricating equipment that employs gas to process semiconductor substrates and the like. More particularly, the present invention relates to a mass flow controller of a gas supplying apparatus of semiconductor device fabricating equipment.
2. Description of the Related Art
Generally, various kinds of gases are used in semiconductor fabricating processes. A mass flow controller measures and controls the mass flows of the gases. Requirements for the accuracy of mass flow controllers have increased to meet the increasing demand for more highly integrated semiconductor devices.
FIG. 1 is a sectional view of a conventional mass flow controller, and FIG. 2 is a is an enlarged view of a mass flow sensor of the conventional mass flow controller.
Referring to FIGS. 1 and 2, a base 110 of the conventional mass flow controller 100 has a passage 112 through which a fluid passes, an inlet portion 114 for introducing the fluid into the passage 112, an outlet portion 116 for releasing the fluid from the passage 112.
A bypass 120 is disposed in the passage 112. The conventional mass flow controller 100 also has a sampling pipe 132 connected to the passage 112 between an inlet of the bypass 120 and an outlet of the bypass 120. Accordingly, a sample of the fluid flowing through the base 110 passes through the sampling pipe 132.
A mass flow sensor 130 measures a mass flow of the fluid passing through the sampling pipe 132 and hence, through the passage 112. The mass flow sensor 130 includes a first thermal resistance 134a and a second thermal resistance 134b wound around the sampling pipe 132. The first thermal resistance 134a and the second thermal resistance 134b include platinum (Pt) or other similar metals are connected to a bridge circuit 136. A control valve 140, e.g., a solenoid valve, is connected between the bypass 120 and the outlet end 116.
When the first thermal resistance 134a and the second thermal resistance 134b are heated, a temperature difference proportional to the mass flow of the fluid is generated between upstream and downstream ends of the sampling pipe 132. As a result, resistance values of the first thermal resistance 134a and the second thermal resistance 134b become different. The bridge circuit 136 detects the different resistance values as an electric signal. The detected signal is amplified through an amplifier (not shown). A compensator correlates the amplified signal to the mass flow of the fluid.
The measured signal indicating the mass flow of the fluid is transmitted to a valve controller (not shown). The valve controller compares the measured signal to a standard signal corresponding to a predetermined desired flow of the fluid. The valve controller moves the control valve 140 until the measured signal corresponds to the standard signal.
As mentioned above, this type of mass flow controller is widely used in apparatus for fabricating a semiconductor device. For example, the mass flow controller is used for controlling the supplying of a reaction gas in equipment in which a deposition process or an etching process is performed on a substrate.
When the mass flow controller malfunctions during the process, a main controller of the substrate processing equipment suspends the process. In particular, the main controller closes a plurality of valves mounted on a gas line through which the reacting gas passes. The substrate is unloaded from the substrate processing equipment. The reacting gas remaining in the gas line and the mass flow controller is then exhausted. Then, the mass flow controller is exchanged.
Accordingly, a gas supplying apparatus connected to the substrate processing equipment includes a purge line and a purge valve for exhausting the reacting gas that remains in the gas line and the mass flow controller. The purge line and the purge valve are connected to an inlet portion of the mass flow controller.
In addition, the control valve 140 of the mass flow controller is held open by current supplied to the control valve. On the contrary, the control valve 140 closes when the current is not supplied to the control valve. Thus, when the main controller cuts off the current to the control valve 140, the control valve 140 blocks the passage 112 in the base 10. Also, when the control valve 140 is experiencing trouble, the reacting gas remaining in the gas line and the mass flow controller is exhausted through only the purge line and the purge valve. However, the purge line and the purge valve contribute significantly to the volume and cost of the gas supplying apparatus